The present invention relates to a process for the preparation of monohalogenated 2-oxo-1,3-dioxolanes of the general formula
C3H3XO3xe2x80x83xe2x80x83(I)
in which
X is Cl or Br,
characterized in that the monohalogenation is carried out starting from ethylene carbonate with sulfuryl dihalides under UV irradiation and in the absence of solvents.
Halogenated 2-oxo-1,3-dioxolanes are added to the solvents in electrochemical cells. They are used to increase the stability of the electrode materials. In addition, they are intermediates for the preparation of vinylene carbonate (II) which is used as an additive in electrolyte solutions for electrochemical cells. The vinylene carbonate acts as a stabilizer for the electrode materials. Vinylene carbonates are obtained by means of an elimination reaction from the monohalogenated 2-oxo-1,3-dioxolanes (I) or else by means of the reaction of dihalogenated compounds (III) with Zn, as described by M. S. Newman in J. Am. Chem. Soc., 77, 3789-3793, (1955). 
Chlorinated 2-oxo-1,3-dioxolanes such as 4-chloro-2-oxo-1,3-dioxolane (I) are usually synthesized by chlorination of the corresponding 2-oxo-1,3-dioxolanes (IV). In U.S. Pat. No. 3,021,340, ethylene carbonate (2-oxo-1,3-dioxolane) is heated to boiling point in tetrachloromethane and anhydrous iron chloride. Chlorine is passed through the solution for 36 hours. Distillative work-up gives a mixture of mono-and dichlorinated dioxolane (I) and (III).
The change in the reaction conditions, such as, for example, irradiation of the reaction solution with a 350 W lamp, leads to a significant shortening of the reaction time (R. G. Finke et al., J. Am. Chem. Soc. (105), 7592-7604, (1983)). In this process too, 4,5-dichloro-2-oxo-1,3-dioxolane (III) is formed in addition to 4-chloro-2-oxo-1,3-dioxolane (I).
The chlorination can be carried out not only using chlorine by irradiation with light at a suitable wavelength, but also using substances which decompose to form free radicals. It has been observed that when sulfuryl chloride is used as the chlorinating agent, small amounts of organic peroxides have activating properties similar to light (M. S. Kharasch et al., Am. Soc., (61), 2142, (1939); (62), 925 ff., (1940)). In G. Wulff et al., Chem. Ber. (125), 473-477, (1992), sulfuryl chloride is used for the synthesis of chlorinated 2-oxo-1,3-dioxolanes. The solution is heated in tetrachloromethane and irradiated with a 500 W lamp. The monochlorinated dioxolane and the dichlorinated dioxolane are isolated.
The use of tetrachloromethane as solvent requires increased safety precautions since this compound is classified as toxic, injurious to health, causing irreversible damage, and harmful to the environment.
The object of the invention was therefore to develop an environmentally friendly and cost-effective process for selectively synthesizing the monochlorinated compound.
The object according to the invention is achieved by a novel process for the preparation of monohalogenated 2-oxo-1,3-dioxolanes of the general formula
C3H3XO3xe2x80x83xe2x80x83(I)
in which
X is Cl or Br,
characterized in that the monohalogenation is carried out starting from ethylene carbonate with sulfuryl dihalides under UV irradiation at temperatures between 0xc2x0 C. and 90xc2x0 C. in the absence of solvents, under atmospheric pressure and in the presence of atmospheric oxygen or optionally under a protective-gas atmosphere.
Experiments have shown that the reaction of the starting compound 2-oxo-1,3-dioxolane (IV) with sulfuryl chloride can be carried out without tetrachloromethane. 
The rate of the reaction proved to be only slightly lower than for the synthesis with tetrachloromethane (CCl4). Surprisingly, it has been found that when equimolar amounts of ethylene carbonate and sulfuryl chloride are used in the process according to the invention, the formation of the undesired dichlorinated by-product is avoided if the process is carried out in the absence of tetrachloromethane.
Additionally, work-up is simplified since neither the solvent nor dichloroethylene carbonate have to be removed by distillation. In the case of further conversion to vinylene carbonate, it is possible to dispense completely with prior work-up since the unreacted ethylene carbonate can be removed by distillation without problem following this further reaction step.
A particular advantage of the process according to the invention is that despite the absence of the solvent, a high reaction rate and high quantitative yield are obtained. In carrying out the process according to the invention, it has also been found that the evolution of gas, i.e. the formation of HCl and SO2, can be regulated by means of the radiation intensity. This makes it considerably easier to carry out the process since it is not necessary to exhaust large amounts of gas within a very short time. Because the gas is evolved considerably more slowly. It is possible to dispense with the batchwise introduction of the starting materials, and it is not necessary to wait for the evolution of gas to subside either. For scaling-up of the reaction, not only is the batchwise procedure possible, but also continuous operation. An advantage of this is the low residence time because of the high rate of reaction. The reaction can be carried out continuously, for example through a cascade of two or more conventional photochemical reactors or thin-film roll photochemical reactors. Because tetrachloromethane is dispensed with as solvent, the authorization procedure for a large-scale industrial plant is considerably simplified. Contrary to implementation procedures to date, the reaction does not have to be carried out under a protective-gas atmosphere. The saving in terms of raw materials, e.g. of solvent and of the protective gas, and the consequently considerably simplified apparatus lead to considerably reduced costs.
For the preparation of monohalogenated 2-oxo-1,3-dioxolanes, a coolable apparatus fitted with appropriate equipment for monitoring the temperature in the reaction vessel, a gas inlet and outlet line, a mixing device, and equipment for generating UV radiation, such as, for example, a high-pressure mercury vapour lamp, is required. The apparatus can be connected upstream of gas-scrubbing equipment, for the absorption of HCl and SO2.
To carry out the process according to the invention, ethylene carbonate and sulfuryl dihalides are introduced into the apparatus and exposed under a pressure which is atmospheric or slightly above atmospheric and in the presence of atmospheric oxygen or optionally under a protective-gas atmosphere. The temperature in the reaction vessel is maintained at between 0xc2x0 C. and 70xc2x0 C. by means of iced-water cooling or a cryostat or the like. The reaction kinetics are good at temperatures between 20xc2x0 C. and 70xc2x0 C. The exposure time is variable and is between 15 and 300 min, depending on the intensity of the radiation and the desired conversion. For a batchwise addition of the sulfuryl chloride and an exposure time of 30 min, a yield of monohalogenated 2-oxo-1,3-dioxolane of 79% was achieved. A continuous, equimolar metered addition of sulfuryl halide offers the advantage that the gas is evolved in a controllable manner. The exposure time can thus be reduced to from 15 to 60 min. It is therefore possible for the person skilled in the art to choose, analogous to the amounts of starting materials used, the corresponding parameters such as temperature and exposure time so that they are optimal. Surprisingly, when the reaction was carried out using equimolar amounts, no traces of a dihalogenated by-product were found. Distillative work-up is simplified since only unreacted starting material has to be removed, and not by-products and solvent.